Abstract
N-containing gaseous compounds, such as trimethylamine (TMA), triethylamine (TEA), ammonia (NH3), nitrogen monoxide (NO), and nitrogen dioxide (NO2) exude irritating odors and are harmful to the human respiratory system at high concentrations. In this study, we investigated the sensing responses of five sensor materials—Al-doped ZnO (AZO) nanoparticles (NPs), Pt-loaded AZO NPs, a Pt-loaded WO3 (Pt-WO3) thin film, an Au-loaded WO3 (Au-WO3) thin film, and N-doped graphene—to the five aforementioned gases at a concentration of 10 parts per million (ppm). The ZnO- and WO3-based materials exhibited n-type semiconducting behavior, and their responses to tertiary amines were significantly higher than those of nitric oxides. The N-doped graphene exhibited p-type semiconducting behavior and responded only to nitric oxides. The Au- and Pt-WO3 thin films exhibited extremely high responses of approximately 100,000 for 10 ppm of triethylamine (TEA) and approximately −2700 for 10 ppm of NO2, respectively. These sensing responses are superior to those of previously reported sensors based on semiconducting metal oxides. On the basis of the sensing response results, we drew radar plots, which indicated that selective pattern recognition could be achieved by using the five sensing materials together. Thus, we demonstrated the possibility to distinguish each type of gas by applying the patterns to recognition techniques.
Highlights
Many N-containing gases exude irritating odors, such as ammonia (NH3 ), trimethylamine (TMA), triethylamine (TEA), nitric oxide (NO), and nitrogen dioxide (NO2 )
The isolated Al-doped ZnO (AZO) NP represented the single crystallinity of a hexagonal wurtzite structure of ZnO with a lattice spacing of ~0.28 nm, which was confirmed by high-resolution TEM analysis with the electron diffraction pattern [54]
~2 nm were uniformly distributed on the surface of the AZO NPs, which was confirmed by analyses of the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and the energy dispersive X-ray spectroscope (EDS) line profile [54,55]
Summary
Many N-containing gases exude irritating odors, such as ammonia (NH3 ), trimethylamine (TMA), triethylamine (TEA), nitric oxide (NO), and nitrogen dioxide (NO2 ). NH3 mainly arises from natural sources through the decomposition of organic matter containing nitrogen. Exposure to high levels of NH3 emitted from chemical plants, cultivated farmland (fertilizer), and motor vehicles can cause irritation and serious burns on the skin and in the mouth, throat, lungs, and eyes [1,2]. TMA is a colorless, hygroscopic, and flammable tertiary amine that has a strong fishy odor at low concentrations and an NH3 -like odor at higher concentrations. Exposure to high levels of TMA can cause headaches, nausea, and irritation to the eyes and respiratory system.
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